Hi Ken:

Sound to me like a classic RF in the shack problem. With the two mag-mount
antenna that close to the rest of the station RF pick up seems like a sure
thing. When you move your bit of ground braid around your changing the
electrical length outside of the coax. Any wire over a few inches long is
not a RF ground.


--
John Passaneau
Penn State University, State College Pa.
W3JXP


"Ken Bessler" wrote in message
...
I'm trying to understand a grounding situation at myt ststion. Here
is the station layout:

Pyramid Phase III 25 amp power supply feeding power to all
devices. First there is the radio - a Yaesu FT817. The antenna
output from this goes to a 2 position antenna switch. One side
of the switch feeds directly to a high perormance 2m/440 dual
band mag mount antenna on my A/C unit. The other side goes
to a MFJ 1040B rf preselector (also powered by the Pyramid).
The preselector has 2 antenna outputs - one goes to a Rat shack
11 meter "high performance" mag mount antenna (tuned for 10m)
also on my A/C unit. The other output goes to a LDG Z11
autotuner. The output from the tuner goes to a 34' long inverted
V antenna outside my window (I'm on the 3rd floor).

All these devices share a common ground through either the
coax shield or DC power ground or both. I have yet to install
a proper station ground for the whole setup and I don't know
if the power supply is grounded properly at the 115v ac outlet.

There - now that that is said, here is the problem:

When tuned on any band, my SWR gets better if I touch the
case of the tuner. I then installed a 1/4" braid from the tuner's
chassis screw to the ground lug on the antenna switch and that
solved the problem. I moved the braid from the antenna switch
to the case of the MFJ 1040B and the same thing happened
but not nearly as good as the effect I got when hooked to the
antenna switch.

I thought the coax sheild was a good ground path - how
could installing a ground line between the tuner and the
switch help? All chassis's are metal except for the sides of
the MFJ 1040B preselector. All patch coax cables have been
swapped out with others with no changes seen. The system
as a whole seems to operate well - on 10 m the mag mount
works best. Below that the inverted V works better. Although
the Z11 can't autotune below 5 mhz, I can manually tune and
get a good SWR down to 1.8 mhz with the Z11 in manual mode.

Grounding will be easy when I get around to it - I have
baseboard hot water radiators that I can ground to.

Any ideas, folks?

72's de Ken KG0WX